Just a note on terminology, as folks seem to be confusing moles with
gophers:
Moles are insectivores -- basically subterranean shrews. They primarily
eat worms, grubs, and other arthropods living in the soil. Their tunnels
may uproot plants, but they're unlikely to do much munching on roots or
any other part of your plants.
Gophers, on the other hand, are rodents, and will eat plenty of
vegetation. In some parts of North America they can do a lot of damage
to one's garden. My in-laws (northern Willamette Valley, Oregon) have
plenty of gophers, and occasionally they'll notice that certain plants
have gone missing entirely. Upon further observation, they find that the
gophers have pulled the entire plant down into their tunnels to get at
the nice green bits that grow above ground. The stories I've heard from
folks who have lots of gophers suggest that there are no really
effective ways of controlling or eliminating them. Gopher plant (castor)
doesn't work (they won't eat it, but it won't keep them from anything
around it), predators (cats and dogs) can get at them only on the rare
occasion that they surface (maybe ferrets would do better?), and sonic
devices (thumpers) seem generally to annoy people more than they do
gophers. Traps will kill some of them, but they breed and recolonize a
lot faster than they can be trapped. Also, some traps (the ones that
fire a bullet into the ground) have a bad tendancy to misfire and do
extensive injury to the person setting them -- and they're probably
illegal in most places.
My suggestion would be to experiment a bit ... gophers really seem to
like certain plants more than others. Out of the 18 gopher species in
the US and Canada, 13 of them have very localized ranges. The camas
pocket gopher, for example, is found only in the Willamette Valley of
Oregon. Texas has around 10 species. This high localization suggests
that they might also be fairly specialized in terms of diet, sort of
like Darwin's finches in the Galapagos, but on a larger scale. One could
try planting a wide variety of plants and keep careful track of which
species and varieties get heavily munched and which are avoided.
On the other hand, one could discover that the "standard" garden
vegetables are all on the gophers' "delicacies" list. Another
possibility would be to create raised beds and enclosing the sides and
bottom with a fairly fine-grade wire mesh down to a depth of a couple
feet... this would be a labor-intensive method only suitable for a small
area.
One last suggestion would be to leave plenty of brush, mulch, and rock
piles around to provide habitat for snakes. Never underestimate the
value of a good reptile. Of course, if one is living in an area where
poisonous snakes are common, one might not want to encourage their
presence close to heavily-frequented areas like the home and garden.